1. Field of the Invention
This invention relates to containers and more particularly to special containers for asphalt and asphalt compositions.
2. Description of the Prior Art
As is well known in the art molten asphalt is employed for various jobs in the construction arts such as for seal coating roadways, runways and the like, and also for comparatively small jobs such as the filling of cracks and expansion joints in paved surfaces, and various spot applications such as on paved surfaces, roofs, and the like.
In the relatively large jobs, such as the above mentioned seal coating of paved surfaces, where large quantities of molten asphalt are to be used, the molten asphalt is placed in special transport trucks at the asphalt plant and delivered directly to the job site where it is transferred either to interim storage tanks or directly to heated spray applicator trucks. In some instances, the molten asphalt is mixed at the job site with special additives such as shredded rubber, prior to being applied to the paved surface. At any rate, such a procedure must be accomplished rather rapidly to prevent excessive cooling of the molten asphalt, to keep the needed interim storage facilities to a minimum, and to keep equipment and labor costs to a minimum. Even when this procedure is most efficiently accomplished, it is an expensive matter and as such cannot be economically justified on the comparatively smaller jobs due to the smaller quantities of materials needed, the slow and often interrupted application schedules and the like.
Therefore, it is common practice to place molten asphalt, or molten asphalt compositions, in manually handleable containers at a manufacturing facility and ship the desired quantity to a job site on an as needed and when needed basis. When the asphalt is needed at a job site, the containers are torn open and the asphalt, which has since cooled and thus, solidified, is placed in a heating vessel which is usually a tank which is an integral part of the mechanism which is to be used to apply the asphalt. When the desired temperature of the molten asphalt is reached, normally a minimum of about 275.degree. F., it is applied in accordance with procedures suitable for the particular job.
As is known, molten asphalt is a difficult material to handle due to the inherent characteristics of the material itself which, in addition to the prior art containers commonly used in the packaging thereof, makes the containerization of the molten asphalt a slow, messy and relatively costly operation.
Molten asphalt will flow at temperatures as low as about 200.degree. F. but is very viscous at such low temperatures which makes the pumping thereof a slow and otherwise difficult task. At higher temperatures, the molten asphalt will, of course, become less viscous and thus is easier on the pumps and otherwise makes the filling of the containers a faster, easier, and less costly operation.
However, at the elevated temperatures at which the molten asphalt will more easily flow, such elevated temperatures can destroy the containers. Thus, prior art containerization of molten asphalt is accomplished at compromise temperatures, which to the best of my knowledge, have never exceeded about 225.degree. F. without melting the containers commonly used in the art. It will be seen from the above that a limiting factor in the prior art asphalt containerization process is the container itself which requires that the asphalt be cooled from about the 350.degree. F. temperature at which it is received from the asphalt plant to about 225.degree. F., or lower, so that it will not destroy the containers. Such cooling can involve a considerable time delay particularly in warm climates in that such a large quantity of molten asphalt does not cool rapidly.
Therefore, due to the required cooling time and the relatively low temperatures at which the prior art containerization of molten asphalt must be accomplished, it will be seen that the prior art method is a slow and costly operation both from a labor standpoint and an equipment wear standpoint.
Another characteristic of the asphalt which must be considered in all containerization processes is that asphalt will adhere to virtually anything and upon cooling will form a very tenacious bond with the contacted item. This inherent characteristic of asphalt has dictated the basic design parameters of the containers used since the beginning of this type of containerization.
The conventional container for asphalt includes a corrugated cardboard carton into which a thin-wall bag is inserted as a liner. The thin-wall liner bag is formed of a synthetic plastic material having a wall thickness of about 0.006 inches, and the specific material heretofore used is a low density polyethylene which is capable of withstanding temperatures of up to a maximum of about 225.degree. F. and will melt at or somewhat higher than that temperature.
When the molten asphalt is pumped into the plastic liner bags it will adhere thereto which makes subsequent removal difficult if not impossible to accomplish. Therefore, when readying the containerized asphalt for use at a job site, it is a common practice to tear open the carton, remove the plastic liner bag having the solidified asphalt therein and place it, liner bag and all, in the vessel which is to be used to heat the asphalt. Due to the nature of the plastic material, and since the mass of the plastic is small in comparison to the mass of the asphalt, the plastic will not appreciably affect the integrity of the asphalt. This common practice places further design parameters on the nature and characteristics of the plastic liner in addition to its being capable of withstanding the hereinbefore described containerization temperatures. These further considerations are that the liner bag ideally should be as thin as possible, preferably below the 0.006 inch film thickness commonly used in the prior art, and should melt at asphalt reheat temperatures of about 275.degree. F. which is the ideal temperature at which the molten asphalt will, for example, properly flow into cracks and expansion joints in paved surfaces.
In view of the above, it will be appreciated that the plastic liner bag used for the containerization of asphalt should have as thin a wall thickness as possible to reduce contamination of the asphalt, and should be capable of withstanding temperatures as high as possible to minimize the asphalt precooling time and otherwise result in maximum containerization efficiency. Further, the material of which the plastic liner bag is formed must be completely molten at the temperature to which the asphalt is reheated at the job site for application purposes. To the best of my knowledge, no prior art asphalt container has been developed which meets these desired characteristics.
Therefore, a need exists for a new and improved manually handleable container for asphalt and asphalt compositions, which overcomes some of the problems and shortcomings of the prior art.